Tokkai Hei 09-150641 published by the Japan Patent Office in 1997 discloses a differential for a four-wheel drive vehicle based on a front-wheel drive vehicle.
This differential is formed in a differential housing fixed to a transmission case. A differential case is supported free to rotate in the differential housing via a bearing. A ring gear which meshes with the output gear of the transmission, and a hollow shaft to spline-joint the output shaft, are coaxially fixed to the differential case.
In the differential case, a pair of pinions are supported free to rotate via a pinion shaft. A pair of side gears that mesh with these pinions are housed in the differential case. Each side gear has a sleeve which is spline-jointed to an axle shaft of the front wheels. The rotation of a ring gear is transmitted to a transfer via an output shaft, and transmitted from the transfer to the rear wheels.
The rotation of the ring gear is also distributed to the side gears via the pinions in the differential case, and transmitted to the front wheels via the axle shafts.